<htmml>
    <head></head>
    <body>
        <div>
            <div id="div1">
                <div id="div2"></div>
            </div>
        </div>
    </body>
</htmml>
<style>
    #div1{
      border: red 7px solid;
      clear: both;
    }
    #div2{
    width: 200px;
    height: 200px;
    background-color: green;
    float: left;
    }
    #div1:after{
        content: "aaa";
        display: block;
        clear: both;
    }
</style>
<script>
</script>